RADI-08. Elucidating the Electrophysiology of Intraoperative Radiotherapy – Experience from Two Cases

Brain metastases require multimodality treatment, often combining surgical resection, radiation therapy, and individualized systemic pharmacotherapy based on oncogenic drivers. Intraoperative radiation therapy (IORT) is an emerging treatment option where radiation is delivered directly to the resection cavity at the time of surgery. We present two patients who underwent electrocorticography (ECoG) during IORT, providing information regarding electrophysiologic safety and tolerability of the technique. In the first case, a 65-year-old woman underwent resection of a hemorrhagic right occipital metastasis from non-small cell lung cancer. IORT was administered over sixteen minutes for a surface dose of 30 Gy. In the second case, a 73-year-old man with underwent resection of a right posterior frontal metastasis from non-small cell lung cancer. IORT was delivered over eleven minutes for a surface dose of 30 Gy. In both cases, a 1x6 contact array of subdural electrodes was placed adjacent to the planned field of radiation. Electrocortigraphy (HFF 70 Hz, TC 0.3 sec, sensitivity 150uV/mm) was obtained from the array two minutes prior to initiation of therapy, during therapy, and two minutes after completion of therapy in both cases. We found that IORT did not induce electrophysiological change in the tissue surrounding it in both cases with no epileptiform or ictal discharges during 20 minutes of ECoG recording around the time radiation therapy, nor did the patients have episodes suggestive of epileptic seizures in the acute post-operative period. One of the patients (case 1) experienced a single epileptic seizure 4 months after IORT, but this was temporally related to a new intraparenchymal hemorrhage and unlikely due to radiation therapy. These two cases illustrate the relative safety of IORT with respect to induction of immediate epileptiform changes within the brain parenchyma.